PLANT PHYSIOLOGY , Vol 115, Issue 4 1651-1659, Copyright © 1997 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Carbon Partitioning during Sucrose Accumulation in Sugarcane Internodal Tissue
A. Whittaker and F. C. Botha
Department of Biotechnology, South African Sugar Association Experiment Station, Mount Edgecombe, KwaZulu-Natal 4300, South Africa (A.W., F.C.B.)
The temporal relationship between sucrose (Suc) accumulation and carbon
partitioning was investigated in developing sugarcane internodes.
Radiolabeling studies on tissue slices, which contained Suc concentrations
ranging from 14 to 42% of the dry mass, indicated that maturation coincided
with a redirection of carbon from water-insoluble matter, respiration,
amino acids, organic acids, and phosphorylated intermediates into Suc. It
is evident that a cycle of Suc synthesis and degradation exists in all of
the internodes. The decreased allocation of carbon to respiration coincides
with a decreased flux from the hexose pool. Both the glucose and fructose
(Fru) concentrations significantly decrease during maturation. The
phosphoenolpyruvate, Fru-6-phosphate (Fru-6-P), and Fru-2,6-bisphosphate
(Fru-2, 6-P2) concentrations decrease between the young and older
internodal tissue, whereas the inorganic phosphate concentration increases.
The calculated mass-action ratios indicate that the ATP-dependent
phosphofructokinase, pyruvate kinase, and Fru-1,6-bisphosphatase reactions
are tightly regulated in all of the internodes, and no evidence was found
that major changes in the regulation of any of these enzymes occur. The
pyrophosphate-dependent phosphofructokinase reaction is in apparent
equilibrium in all the internodes. Substrate availability might be one of
the prime factors contributing to the observed decrease in respiration.
